1. Field of the Invention
The present invention relates to a signal processing apparatus, a signal processing method, and a program. More specifically, the present invention relates to a signal processing apparatus, a signal processing method, and a program, capable of correctly determining a value of a symbol represented by a signal.
2. Description of the Related Art
In a related art, a signal processing apparatus receives an image signal from an external device such as a tuner adapted to receive a television broadcast signal or a DVD (Digital Versatile Disc) player, processes the received image signal, and supplies the resultant image signal to a display such as a CRT (Cathode Ray Tube) or a LCD (Liquid Crystal Display).
The signal processing performed by such a signal processing apparatus includes, for example, a process of removing noise from the image signal supplied from an external device, a process of converting an image signal supplied from an external device into a form having higher quality than the original quality, and a process of adjusting brightness or contrast of an image displayed on a display.
FIG. 1 is a block diagram illustrating an example of a configuration of a signal processing apparatus.
As shown in FIG. 1, the signal processing apparatus 11 includes a case 12, connectors 131 to 134, an input selector 14, a signal router 15, connectors 161 to 164, connectors 171 to 173, functional blocks 181 to 183, a connector 19, a remote commander 20, an operation unit 21, a system control block 22, and a control bus 23.
In the signal processing apparatus 11, the connectors 131 to 134 are connected to the input selector 14 via signal cables, and the input selector 14 is connected to the signal router 15 via a signal cable. The signal router 15 is connected to the connectors 161 to 164 and the connector 19 via signal cables. The signal router 15 is connected to the functional blocks 181 to 183 via the connectors 161 to 163 and the connectors 171 to 173. The input selector 14, the signal router 15, the connectors 161 to 164, and the system control block 22 are connected to each other via the control bus 23.
The case 12 is formed in the shape of, for example, a rectangular box. On the outer surface of the case 12, the connectors 131 to 134, the connector 19, and the operation unit 21 are disposed. In the inside of the case 12, the input selector 14, the signal router 15, the connectors 161 to 164, the connectors 171 to 173, the functional blocks 181 to 183, the system control block 22, and the control bus 23 are disposed.
The connectors 131 to 134 are for a connection, via a cable, between the signal processing apparatus 11 and an external apparatus (not shown) such as a tuner or a DVD player from which an image signal is supplied to the signal processing apparatus 11.
Image signals are supplied from external apparatuses to the input selector 14 via the connectors 131 to 134. Under the control of the system control block 22, the input selector 14 selects one of image signals supplied from the external apparatuses via the connectors 131 to 134, and the input selector 14 supplies the selected image signal to the signal router 15.
Under the control of the system control block 22, the signal router 15 supplies the signal received via the input selector 14 to the functional blocks 181 to 183 the connectors 161, to 163 and the connectors 171 to 173. The functional blocks 181 to 183 perform signal processing on the signals and return the resultant signals to the signal router 15. The signal router 15 transfers the received signals to a display (not shown) connected to the connector 19.
The connectors 171 to 173 are connectable/disconnectable to/from the connectors 161, to 163 so that the functional blocks 181 to 183 are connected to the signal router 15 or the control bus 23. The connector 164 is for future use of a connection with a new functional block or the like which will be added to the signal processing apparatus 11.
The functional blocks 181 to 183 include a signal processing circuit for noise reduction, image conversion, or image correction. The functional blocks 181 to 183 perform signal processing on the signal supplied from the signal router 15 and return the resultant signal to the signal router 15.
The connector 19 is for connecting, via a cable, the signal processing apparatus 11 to the display for displaying an image in accordance with the image signal output from the signal processing apparatus 11.
The remote commander 20 includes a plurality of buttons or the like. If a button is operated by a user, an operation signal depending on the operated button is transmitted in the form of an infrared ray or the like to the system control block 22.
The operation unit 21 includes a plurality of buttons or the like, as with the remote commander 20. If a button is operated by a user, an operation signal depending on the operated button is supplied to the system control block 22.
If the system control block 22 receives the operation signal generated depending on the operation of the user from the remote commander 20 or the operation unit 21, the system control block 22 controls the input selector 14, the signal router 15, and the functional blocks 181 to 183 via the control bus 23 so that a process is performed in accordance with the operation signal.
In the signal processing apparatus 11, as described above, an image signal is supplied to the signal router 15 via the connectors 131 to 134 and the input selector 14, and an image signal is transmitted between the signal router 15 and functional blocks 181 to 183 via signal cables.
A recent trend is toward an increase in resolution of images. Accordingly, the data size of the image signal processed by the signal processing apparatus 11 tends to increase. To handle image signals with great data sizes, it is necessary to transmit image signals at a high rate between the signal router 15 and the functional blocks 181 to 183 via cables. However, the increase in the signal transmission rate can create problems associated with frequency characteristics of signal cables, crosstalk, a difference in signal propagation timing (skew) between parallel signal cables, etc.
Japanese Unexamined Patent Application Publication No. 2003-179821 discloses a signal processing apparatus adapted to transmit signals by wireless communication using an electromagnetic wave among circuit boards disposed in a case thereby performing signal processing.
Use of wireless transmission using electromagnetic waves between the signal router 15 and the functional blocks 181 to 183 makes it possible to avoid the problems which can occur when signals are transmitted at high rates via signal cables.
However, if signals are transmitted by wireless communication using electromagnetic waves between signal router 15 and the functional blocks 181 to 183 in the inside of the case 12 of the signal processing apparatus 11, a plurality of transmission paths (multi-path) which are different in length can occur due to reflection of electromagnetic waves from walls of the case 12 or due to diffraction of electromagnetic waves by circuit boards disposed in the case 12. The signal transmission via multiple paths can shift the phase of the signal arriving at the receiving part, and thus interference between symbols represented by signals (electromagnetic waves) can occur.
If such intersymbol interference occurs, signal values of symbols transmitted before a particular symbol can influence the signal value of the particular symbol, and thus the signal value of this particular symbol can change (this phenomenon is called multipath fading). If the signal value of a symbol is changed as a result of influence of other symbols, it is difficult for the receiving part to determine the correct symbol value of the received symbol. For example, in a case where one bit is transmitted by one symbol, it is difficult to correctly determine which one of 1 and 0 is originally intended by the symbol.
The problem associated with the multipath interference can occur not only in wireless communication within a case, but also in mobile communication between portable telephone devices due to a shift in signal phase caused by multipath produced by reflection of electromagnetic waves from buildings. Interference can also occur between an original signal propagating along a cable and a signal reflected by an end of the cable.
For example, Japanese Patent No. 3399022 discloses a technique to use a Vitabi equalizer to remove interference due to multipath.
In the signal processing on signals transmitted at a high rate as with signal processing on the image signal (in particular on non-compressed image signals), it is required that a delay occurring during the signal processing should be short enough and the delay should be controlled at a constant value. However, the Vitabi equalizer creates a large delay, and the created delay is not constant. Besides, in the signal processing on image signals, it is required to perform the signal processing continuously in real time. However, it is difficult to perform process associated with the Vitabi equalizer in real time.